FR2554433A1 - PROCESS FOR THE PREPARATION OF A HYDROGEN-RICH GAS - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A PROCESS FOR THE PREPARATION OF A GAS RICH IN HYDROGEN, WHICH IS CARRIED OUT BY TRANSFORMING A GAS CONTAINING CARBON OXIDE WITH WATER VAPOR. THE CONVERSION IS CARRIED OUT IN THE PRESENCE OF A CATALYST CONTAINING A SPINEL WHOSE COMPOSITION CORRESPONDS TO THE LICU (1-X) FEO FORMULA IN WHICH 0X1. PREFERABLY, AN ALKALINE METAL COMPOUND IS ADDED TO THE CATALYST. APPLICATION TO INDUSTRIAL PROCESSES FOR THE PREPARATION OF HYDROGEN.

Description

The present invention relates to a process for the preparation of a gas

  rich in hydrogen made by transforming a gas containing carbon monoxide with

  water vapor in accordance with the reaction of

version of the gas with water:

CO + H20> CO2 + H

2 2 2

  This conversion, which is an important part of most industrial processes for the preparation of hydrogen, is generally carried out in two stages in the presence of a catalyst. The first conversion step, which is performed at a temperature of 300 C, is called

  conversion reaction of gas to water at high temperature.

  In the second conversion step, the reaction of

  low temperature gas, a temperature below 300 C is used. Since most of the catalysts proposed so far for the gas-to-water conversion reaction are only sufficiently effective in a rather limited temperature range, it is common practice to use different catalysts in each

  two conversion steps as mentioned above.

  It has now been found that some spinels are excellent catalysts for the reaction of gas-to-water conversion in high temperature operations.

only low.

  The invention therefore relates to a process for preparing

  hydrogen-rich gas, which is carried out by converting a gas containing carbon monoxide with water vapor, characterized in that the conversion is carried out in the presence of a spinel-containing catalyst whose composition corresponds to LixCu (lx) Fe508 in

which 0 <x <1.

  The catalysts used according to the invention are obtained conveniently by mixing a mixed powder of the constituents containing the metals together with water or by precipitating the constituents containing the metals in the desired proportion from a solution of their salts, preferably a solution of carbonates and / or nitrates, by drying the kneaded paste or the precipitate and then calcining the dried pulp or the precipitate, preferably at a temperature of 400 to 1000 ° C. for a period of 3 to 20 hours. hours. It has further been found that it is possible to stabilize the aforementioned catalysts by adding a compound of at least one metal

  alkaline. Catalysts containing these constituents

  serve their activity longer in service, and as

  As a result, it is less frequently necessary

  to replace or replace them. It is advantageous to use catalysts containing from 0.1 to 15% by weight of Li, Na,

  K, Rb and / or Cs, by calculating on the basis of their oxides.

  During the process of converting the gas to water, the alkali metals are preferably present on the catalyst under

  the shape of their oxides and / or their carbonates.

  The catalysts mentioned above can be used as such: they will advantageously be used in the form of particles having a length and / or a diameter of 0.2 to 0.6 mm. However, it is also possible to precipitate the catalysts on a support and use them on this support, after drying and calcination, for the conversion reaction of the gas with water. If desired, aluminum trioxide may be used as a support; suitably, the amount of support will be such that it constitutes from 40 to 80% of the weight of the

total catalyst.

  The conversion reaction of the gas with water, which in principle can take place at temperatures between and 500 C, is generally carried out in practice in several stages, for reasons of reaction speed and equilibrium state. , in part above 300 C (gas-to-water reaction at elevated temperature) and partly below 300 C (reaction of gas-to-water conversion at low temperature) . Preferably, the reaction is carried out by passing the gas to be converted through two or more reactors at temperatures between 300 and 500 C, these reactors containing a catalyst for the reaction of gas conversion to water at high temperature, and then passing the partially converted gas mixture through a reactor at a temperature between 300 ° C and 300 ° C, this reactor containing a catalyst for the low temperature gas-to-water conversion reaction. If the process of converting the gas to water is applied at several stages at different temperatures, partly above and partly below 300 C, a process according to the invention is in any case preferred for step at low temperature. Since the catalysts to be used according to the invention generally have sufficient activity and stability also above 300 ° C., it is advantageous to use a catalyst according to

  the invention in all stages of the reaction of con-

  version of the gas to water, both above and below

300 C.

  The pressure at which the gas-to-water conversion reaction is conducted can vary within wide limits. The reaction is preferably carried out at a pressure of between 10 and 100 bar, in particular between 20 and 80 bar. The amount of water vapor present in the gas mixture subjected to the gas-to-water conversion reaction is preferably 0.5 to 50 mol per

mole of carbon monoxide.

  The rate at which the gas to be converted is passed over the catalyst may vary within wide limits, but is preferably from 1500 to 4500 liters of gas per hour per liter of catalyst at temperature and pressure.

normal.

  As already mentioned, the preparation of hydrogen-rich gas by conversion of a gas containing carbon monoxide with water vapor according to the conversion reaction of gas to water forms an important part of most industrial processes for the preparation of hydrogen. The process according to the invention is very useful as part of such a process for the preparation of hydrogen. The gas containing carbon monoxide is generally obtained in these processes by incomplete combustion of a hydrocarbon or a mixture of hydrocarbons with oxygen. It is preferred to add

  water vapor as a modifying agent to the mixture.

  Incomplete combustion gives a raw gas that includes

  mainly carbon monoxide and hydrogen.

  The hydrocarbon mixture used is preferably a petroleum fraction. Oil fractions of both

  residual distillation can be used for this purpose.

  Under certain conditions, coal, for example in the form of a slurry in a hydrocarbon oil, can also be used as a filler. It is common in most processes to remove heat from the raw gases leaving the combustion reactor and are at a high temperature.

very high temperature.

  This can be done very conveniently by exchanging heat between the gases and water in a waste heat recovery boiler; as a result, high pressure water vapor is formed and the temperature

raw gas is lowered.

  Depending on the starting material chosen and the conditions used in the combustion reactor, the gas thus cooled, which is still at a temperature

  relatively high, may contain a considerable amount

soot.

  Due to the rapid soiling of the catalyst with soot, the soot must be removed from the gas before -5-. to be subjected to the catalytic conversion reaction

  from gas to water, using a conventional reactor.

  However, recently there is a reactor that allows the transformation of gases containing solid impurities, such as soot, without the catalyst quickly becoming fouled by solid impurities. In this reactor, which contains hollow channels for gases in which the gas circulates and whose walls are permeable

  to gases, the catalyst is present behind the walls.

  This reactor is based on the principle that the constituents to be transformed present in the gas are propagated from the gas channels, through the walls of these channels, come into contact with the catalyst, and

  return to the gas channels after conversion.

  The reactor described above is extremely useful

  sand if the carbon-containing gas to be trans-

  forming in the process according to the invention contains soot. Depending on the soot content of the gas, some of the soot may, if desired, be separated from the gas at

advance.

  After completion of the gas conversion reaction

  to water, the hydrogen-rich gas resulting for the pre-

  paration of pure hydrogen must be purified again. If the raw gas mixture leaving the combustion reactor contained sulfur and / or soot, while the sulfur and / or soot were not removed or removed

  only a part of the soot before the reaction of

  version of the gas with water, the sulfur and / or the soot have yet to be eminated from the gas containing hydrogen. The purification of the hydrogen-rich gas also includes in particular the elimination of the carbon dioxide formed

  and unconverted carbon monoxide.

  The following non-limiting examples will show well

  how the invention can be implemented. -

-6-

Example 1

  A catalyst having a composition as defined by the formula Li0.2Cu0.8Fe508 was prepared by grinding 1.847g of Li2CO3, 14.31g of Cu2 (O) and 89.83g of anhydrous Fe203 and 50.50g of Fe. (NO3) 3.9H20 to obtain a powder and drying the resulting paste at 110 C for 3 hours. The mass was then calcined for 1 hour

at 400 C and 2 hours at 800 C.

  By X-ray diffraction, it has been found that

  The resulting mixed oxides had crystallized

line of a spinel.

  The calcined material was sieved and particles with a diameter between 0.4 and 0.6 mm were used for the conversion of carbon monoxide to hydrogen with

water vapor.

  For this purpose, a gas having the following composition was passed, together with water vapor, on a bed formed by the catalyst particles:% by volume

CO 6

CO2 29

H2 65

  The following reaction conditions were used: Temperature 250 C Pressure 40 bar Spatial velocity 1,500 liters at normal temperature and pressure per liter of catalyst per hour Mole ratio steam / gas (V / V) 0.65 34% carbon monoxide present in the gas has been converted during the process according to the following reaction:

CO + H20> H2 + CO

-7-

Example 2

  A catalyst having a composition as defined by the formula: Li0.2Cu0 8Fe508.6K20 (parts by weight) was prepared using the same procedure as in Example 1, followed by impregnation of the resulting ferrite with a aqueous solution of K2CO3, the drying of ferrite impregnated at 200 C and finally its calcination

for 2 hours at 500 C.

  The calcined material was sieved and particles with a diameter of 0.4 to 0.6 mm were used for the conversion of carbon monoxide to hydrogen with water vapor, using the same conditions of

  reaction as described in Example 1.

  In this case, 63% of the carbon monoxide present in the gas was converted in the process, which shows the advantageous effect of the addition of an alkali metal compound on the activity of the catalyst. low temperature.

Example 3

  In this example, the catalyst used in Example 2 was used for the conversion of carbon monoxide with water vapor at higher temperature.

high: 350 C.

  The composition of the gas was the same as in Example 1 and the following reaction conditions were used: Temperature 350 C Pressure 40 bar Space velocity 1500 liters at normal temperature and pressure per liter of catalyst and per hour Vapor mole ratio water / gas (V / V) 0.65

  % of the CO present in the feed gas has been trans-

  formed during the process according to the reaction

CO + H20 -> H2 + CO

  which shows the good activity of the catalyst activated by

  an alkali metal oxide at an elevated temperature.

-8-

Example 4

  A catalyst having a composition as defined by the formula 90Li0.2Cu0.8Fe508.10K20 (parts by weight) was prepared using the same procedure as in Example 2. The calcined material was sieved and the particles of a diameter of 0.4 to 0.6 mm was used for the conversion of carbon monoxide under the same conditions as in Example 3. 62% of the present CO

  in the load has been transformed during the process according to

  in response to CO + H 2 O -> H + CO2 mmntlarati CO + 2 0> 2 + C 2 which indicates the still better activity of the catalyst at elevated temperature if its alkali metal content

been increased.

_9-

Claims (7)

  1. A process for the preparation of a gas rich in   hydrogen, which is carried out by converting a gas con-   containing carbon monoxide with water vapor, characterized in that the conversion is carried out in the presence of a spinel-containing catalyst whose composition corresponds to the formula LixCu (t x) Fe508 in which 0 <x <1.   2. A process according to claim 1, characterized in that the catalyst also contains a compound of at least an alkali metal.   3. A process according to claim 2, characterized in that the catalyst contains from 0.1 to 15% by weight of an alkali metal, calculated in the form of its oxide.   4. A process according to one of claims 1 to 3,   characterized in that the catalyst contains a carrier.   5. A process according to claim 4, characterized in that the support content of the catalyst is from 40 to % in weight.   6. A method according to one of the preceding claims   characterized in that the reaction is conducted at a temperature of 175 to 500 ° C, a pressure of 10 to 100 bar, a space velocity of 1500 to 4500 liters of gas per hour per liter of catalyst at temperature and pressure normal and in a molar ratio of steam   of water with carbon monoxide from 0.5 to 50.   7. The hydrogen-rich gas prepared by a process   according to one of claims 1 to 6.